This small addition changes the speed of the players on a more pleasant. Works only on local server. For get incredible speed use alternate attack your gravity gun on any thing. Also you can change player speed inside game, because convar hl2_normspeed works on sv_cheats = 0
Just write in console, for example, hl2_normspeed 5000 and again use alternate attack your gravity gun on any thing, then your speed will change. Enjoy